The Harbor Freight one I owned for all of 10 minutes. I got home, set it up, and the eye relief made it impossible for someone with glasses. Plus, the tripod was like pick-up sticks. I'd rather spend even a LOT more money and get something actually useful. I do think 20-60x is the magnification to shoot for.

Resolution is the key: the ability of the glass to separate two distinct points. Quailty glass is very expensive, and, you'll want big, light gathering, objective lens. 300 isn'y 600 or 1,000 so u might get away with a lesser brand but I'd suggest investing in a Kowa.